The present invention relates to a liquid tank venting system.
Liquid tanks, when they are likely to be moved with the liquid that they contain, are generally equipped with a ventilation system that guarantees environmental safety when the tank is subjected to various stresses: movements in any direction and of any amplitude, thermal stresses, underpressure and overpressure.
This requirement is encountered in the case of fuel tanks, in particular when they are mounted on motor vehicles and when it is essential to prevent liquid fuel from getting out and to manage large gas pressure and volume changes when filling the tank and throughout the time that the liquid is stored in said tank.
Solutions have been developed to solve these problems that use safety valves immersed in the tank, the upper part of the valves passing through a wall of this tank. These valves generally open into a duct that leads to a box or canister containing a substance capable of trapping the liquid vapours present in the gases originating from the tank. However, it is not uncommon that systems of this type have further difficulties due to the fact that, because of the particular operating circumstances, such as sudden movements or excessively high angle of tilt of the vehicle, liquid originating from the tank may nevertheless pass through the barrier of the safety valve and get into the duct leading to the canister, or even reach the latter and disturb the free flow of the vapours.
To remedy this accidental entrainment of liquid out of the tank, thought has been given to providing said valves with an ROV (or Roll Over Valve) device that generally consists of a heavy ball or a spring connected to a float, which closes the valve in case of a vehicle rolling over, waves, etc. It has also been sought to retain the liquid that escapes via the duct leading to the canister by interposing, in this duct, a dead volume intended to act as a container for collecting the liquid and for letting the vapours pass through freely. This dead volume is generally provided with a device that allows it to be drained when the liquid level in the tank drops below a certain limit, said device furthermore preventing the ingress of liquid into said volume when the liquid level in the tank is above this limit. It is therefore also called a drainable container (or DC). Such systems (both with ROV and CV) are, for example, described in Patents EP 1 020 670 and EP 1 172 306 in the name of the Applicant. The drainage devices that are described therein are non-return valves of the umbrella valve type, which are generally based on an elastomer.
The drawback of these systems from the prior art that use a container or chamber that has to be drained at a high flow rate and that is therefore provided with relatively large aperture(s) sealed by non-return valves, is the lack of leaktightness at these valves. This is because, although this leaktightness is better with elastomer-based “flexible” systems (as in the aforementioned patents in the name of the Applicant), these however have a static leak when the valve remains immersed in the liquid for a prolonged period.